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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        let x = /Hello(?=world)/
        let y = 'Helloworld'
        let z = x.test(y)//检验Hello后面是否是world
        console.log(z)
    </script>
</body>
</html>